On Thu, 1 Jun 2023, Patrick Palka wrote:
> During partial ordering, we want to look through dependent alias
> template specializations within template arguments and otherwise
> treat them as opaque in other contexts (see e.g. r7-7116-g0c942f3edab108
> and r11-7011-g6e0a231a4aa240). To that end template_args_equal was
> given a partial_order flag that controls this behavior. This flag
> does the right thing when a dependent alias template specialization
> appears as template argument of the partial specialization, e.g. in
>
> template<class T, class...> using first_t = T;
> template<class T> struct traits;
> template<class T> struct traits<first_t<T, T&>> { }; // #1
> template<class T> struct traits<first_t<const T, T&>> { }; // #2
>
> we correctly consider #2 to be more specialized than #1. But if
> the alias specialization appears as a template argument of another
> class template specialization, e.g. in
>
> template<class T> struct traits<A<first_t<T, T&>>> { }; // #1
> template<class T> struct traits<A<first_t<const T, T&>>> { }; // #2
>
> then we incorrectly consider #1 and #2 to be unordered. This is because
>
> 1. we don't propagate the flag to recursive template_args_equal calls
> 2. we don't use structural equality for class template specializations
> written in terms of dependent alias template specializations
>
> This patch fixes the first issue by turning the partial_order flag into
> a global. This patch fixes the second issue by making us propagate
> structural equality appropriately when building a class template
> specialization. In passing this patch also improves hashing of
> specializations that use structural equality.
>
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk?
>
> PR c++/90679
>
> gcc/cp/ChangeLog:
>
> * cp-tree.h (comp_template_args): Remove partial_order
> parameter.
> (template_args_equal): Likewise.
> * pt.cc (iterative_hash_template_arg) <case tcc_type>: Hash
> the template and arguments for specializations that use
> structural equality.
> (comparing_for_partial_ordering): New flag.
> (template_args_equal): Remove partial order parameter and
> use comparing_for_partial_ordering instead.
> (comp_template_args): Likewise.
> (comp_template_args_porder): Set comparing_for_partial_ordering
> instead. Make static.
> (any_template_arguments_need_structural_equality_p): Return true
> for an argument that's a dependent alias template specialization
> or a class template specialization that itself needs structural
> equality.
> * tree.cc (cp_tree_equal) <case TREE_VEC>: Adjust call to
> comp_template_args.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp0x/alias-decl-75a.C: New test.
> * g++.dg/cpp0x/alias-decl-75b.C: New test.
Ping. Here's the rebased patch:
-- >8 --
Subject: [PATCH 2/2] c++: partial ordering and dep alias tmpl specs [PR90679]
During partial ordering, we want to look through dependent alias
template specializations within template arguments and otherwise
treat them as opaque in other contexts (see e.g. r7-7116-g0c942f3edab108
and r11-7011-g6e0a231a4aa240). To that end template_args_equal was
given a partial_order flag that controls this behavior. This flag
does the right thing when a dependent alias template specialization
appears as template argument of the partial specialization, e.g. in
template<class T, class...> using first_t = T;
template<class T> struct traits;
template<class T> struct traits<first_t<T, T&>> { }; // #1
template<class T> struct traits<first_t<const T, T&>> { }; // #2
we correctly consider #2 to be more specialized than #1. But if
the alias specialization appears as a template argument of another
class template specialization, e.g. in
template<class T> struct traits<A<first_t<T, T&>>> { }; // #1
template<class T> struct traits<A<first_t<const T, T&>>> { }; // #2
then we incorrectly consider #1 and #2 to be unordered. This is because
1. we don't propagate the flag to recursive template_args_equal calls
2. we don't use structural equality for class template specializations
written in terms of dependent alias template specializations
This patch fixes the first issue by turning the partial_order flag into
a global. This patch fixes the second issue by making us propagate
structural equality appropriately when building a class template
specialization. In passing this patch also improves hashing of
specializations that use structural equality.
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?
PR c++/90679
gcc/cp/ChangeLog:
* cp-tree.h (comp_template_args): Remove partial_order
parameter.
(template_args_equal): Likewise.
* pt.cc (iterative_hash_template_arg) <case tcc_type>: Hash
the template and arguments for specializations that use
structural equality.
(comparing_for_partial_ordering): New flag.
(template_args_equal): Remove partial order parameter and
use comparing_for_partial_ordering instead.
(comp_template_args): Likewise.
(comp_template_args_porder): Set comparing_for_partial_ordering
instead. Make static.
(any_template_arguments_need_structural_equality_p): Return true
for an argument that's a dependent alias template specialization
or a class template specialization that itself needs structural
equality.
* tree.cc (cp_tree_equal) <case TREE_VEC>: Adjust call to
comp_template_args.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/alias-decl-75a.C: New test.
* g++.dg/cpp0x/alias-decl-75b.C: New test.
---
gcc/cp/cp-tree.h | 4 +--
gcc/cp/pt.cc | 40 +++++++++++++++++----
gcc/cp/tree.cc | 2 +-
gcc/testsuite/g++.dg/cpp0x/alias-decl-75a.C | 26 ++++++++++++++
gcc/testsuite/g++.dg/cpp0x/alias-decl-75b.C | 26 ++++++++++++++
5 files changed, 88 insertions(+), 10 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/alias-decl-75a.C
create mode 100644 gcc/testsuite/g++.dg/cpp0x/alias-decl-75b.C
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 85980c9ad9b..1979572c365 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7507,8 +7507,8 @@ extern int template_class_depth (tree);
extern int is_specialization_of (tree, tree);
extern bool is_specialization_of_friend (tree, tree);
extern bool comp_template_args (tree, tree, tree * = NULL,
- tree * = NULL, bool = false);
-extern int template_args_equal (tree, tree, bool = false);
+ tree * = NULL);
+extern int template_args_equal (tree, tree);
extern tree maybe_process_partial_specialization (tree);
extern tree most_specialized_instantiation (tree);
extern tree most_specialized_partial_spec (tree, tsubst_flags_t, bool =
false);
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index a3a79713236..6b0ef496dc5 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -1894,6 +1894,11 @@ iterative_hash_template_arg (tree arg, hashval_t val)
default:
if (tree canonical = TYPE_CANONICAL (arg))
val = iterative_hash_object (TYPE_HASH (canonical), val);
+ else if (tree ti = TYPE_TEMPLATE_INFO (arg))
+ {
+ val = iterative_hash_template_arg (TI_TEMPLATE (ti), val);
+ val = iterative_hash_template_arg (TI_ARGS (ti), val);
+ }
break;
}
@@ -9306,6 +9311,12 @@ coerce_template_parms (tree parms,
return return_full_args ? new_args : new_inner_args;
}
+/* Whether we are comparing template arguments during partial ordering
+ (and therefore want the comparison to look through dependent alias
+ template specializations). */
+
+static int comparing_for_partial_ordering;
+
/* Returns true if T is a wrapper to make a C++20 template parameter
object const. */
@@ -9322,7 +9333,7 @@ class_nttp_const_wrapper_p (tree t)
/* Returns 1 if template args OT and NT are equivalent. */
int
-template_args_equal (tree ot, tree nt, bool partial_order /* = false */)
+template_args_equal (tree ot, tree nt)
{
if (nt == ot)
return 1;
@@ -9345,7 +9356,7 @@ template_args_equal (tree ot, tree nt, bool partial_order
/* = false */)
During partial ordering, however, we need to treat them normally so we can
order uses of the same alias with different cv-qualification (79960). */
auto cso = make_temp_override (comparing_dependent_aliases);
- if (!partial_order)
+ if (!comparing_for_partial_ordering)
++comparing_dependent_aliases;
if (TREE_CODE (nt) == TREE_VEC || TREE_CODE (ot) == TREE_VEC)
@@ -9393,8 +9404,7 @@ template_args_equal (tree ot, tree nt, bool partial_order
/* = false */)
bool
comp_template_args (tree oldargs, tree newargs,
- tree *oldarg_ptr /* = NULL */, tree *newarg_ptr /* = NULL
*/,
- bool partial_order /* = false */)
+ tree *oldarg_ptr /* = NULL */, tree *newarg_ptr /* = NULL
*/)
{
if (oldargs == newargs)
return true;
@@ -9410,7 +9420,7 @@ comp_template_args (tree oldargs, tree newargs,
tree nt = TREE_VEC_ELT (newargs, i);
tree ot = TREE_VEC_ELT (oldargs, i);
- if (! template_args_equal (ot, nt, partial_order))
+ if (! template_args_equal (ot, nt))
{
if (oldarg_ptr != NULL)
*oldarg_ptr = ot;
@@ -9422,10 +9432,13 @@ comp_template_args (tree oldargs, tree newargs,
return true;
}
-inline bool
+static bool
comp_template_args_porder (tree oargs, tree nargs)
{
- return comp_template_args (oargs, nargs, NULL, NULL, true);
+ ++comparing_for_partial_ordering;
+ bool equal = comp_template_args (oargs, nargs);
+ --comparing_for_partial_ordering;
+ return equal;
}
/* Implement a freelist interface for objects of type T.
@@ -28727,6 +28740,19 @@ any_template_arguments_need_structural_equality_p
(tree args)
mutated after the fact by duplicate_decls), so just require
structural equality in this case (PR52830). */
return true;
+ else if (TYPE_P (arg)
+ && TYPE_STRUCTURAL_EQUALITY_P (arg)
+ && dependent_alias_template_spec_p (arg, nt_transparent))
+ /* Require structural equality for specializations written
+ in terms of a dependent alias template specialization. */
+ return true;
+ else if (CLASS_TYPE_P (arg)
+ && TYPE_TEMPLATE_INFO (arg)
+ && TYPE_STRUCTURAL_EQUALITY_P (arg))
+ /* Require structural equality for specializations written
+ in terms of a class template specialization that itself
+ needs structural equality. */
+ return true;
}
}
}
diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index d26e73aaf95..d17b9b34891 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -4131,7 +4131,7 @@ cp_tree_equal (tree t1, tree t2)
case TREE_VEC:
/* These are template args. Really we should be getting the
caller to do this as it knows it to be true. */
- if (!comp_template_args (t1, t2, NULL, NULL, false))
+ if (!comp_template_args (t1, t2))
return false;
return true;
diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-75a.C
b/gcc/testsuite/g++.dg/cpp0x/alias-decl-75a.C
new file mode 100644
index 00000000000..8adbd6f65ac
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-75a.C
@@ -0,0 +1,26 @@
+// PR c++/90679
+// A version of alias-decl-75.C where the specializations of the
+// complex alias template first_t are dependent.
+// { dg-do compile { target c++11 } }
+
+template<class T, class...>
+using first_t = T;
+
+template<class T>
+struct A;
+
+template<class T>
+struct traits;
+
+template<class T>
+struct traits<A<first_t<T, T&>>> {
+ static constexpr int value = 1;
+};
+
+template<class T>
+struct traits<A<first_t<const T, T&>>> {
+ static constexpr int value = 2;
+};
+
+static_assert(traits<A<int>>::value == 1, "");
+static_assert(traits<A<const int>>::value == 2, ""); // { dg-bogus "ambiguous"
}
diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-75b.C
b/gcc/testsuite/g++.dg/cpp0x/alias-decl-75b.C
new file mode 100644
index 00000000000..b89ea5cad1e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-75b.C
@@ -0,0 +1,26 @@
+// PR c++/90679
+// A version of alias-decl-75a.C where the alias template specialization
+// appears as a more deeply nested template argument.
+// { dg-do compile { target c++11 } }
+
+template<class T, class...>
+using first_t = T;
+
+template<class T>
+struct A;
+
+template<class T>
+struct traits;
+
+template<class T>
+struct traits<A<A<first_t<T, T&>>>> {
+ static constexpr int value = 1;
+};
+
+template<class T>
+struct traits<A<A<first_t<const T, T&>>>> {
+ static constexpr int value = 2;
+};
+
+static_assert(traits<A<A<int>>>::value == 1, "");
+static_assert(traits<A<A<const int>>>::value == 2, ""); // { dg-bogus
"ambiguous" }
--
2.43.0.76.g1a87c842ec
